In the prior art, a typical way of assessing the presence of an antigen in a liquid sample is to place the sample in contact with antibodies to the antigen such that when the antibodies bind to the antigen an agglutination of species in the sample occurs. The agglutination is then assessed by optical methods, for example examining optical density, turbidity or light scattering of the sample.
For example, U.S. Pat. No. 6,330,058 discloses a method where the optical density spectrum over a predetermined wavelength range is used to arrive at an agglutination index for the sample. U.S. Pat. No. 5,256,376 also discloses a photometric technique for measuring agglutination by measuring optical density profiles together with an apparatus for use with a centrifuge to carry out the method.
Agglutination tests can be either qualitative, where only the presence or absence of the analyte is detected, or quantitative where the degree of agglutination that has occurred corresponds to a particular level of the analyte. In the prior art the assessment of the agglutination occurring has been performed visually, by using scattered light to measure the solution turbidity or by measuring optical density or the like. These visual techniques, while simple are semi-quantitative at best and open to user error, whereas the optical density or scattering techniques, while more quantitative and less prone to user error, require relatively expensive and complex equipment to be performed.
The present invention seeks to provide an alternative to these prior art techniques.